1. Field of the Invention
This invention relates to a chemical conversion coating formed on a surface of an aluminum substrate; the coating being corrosion-resistant or bacteria-proof or fungiproof, and the surface belonging to a heat exchanger, etc.
2. Description of the Related Art
The forming of a corrosion-resistant coating on a surface of an aluminum product such as an aluminum heat exchanger is known. For example, Japanese Patent Application Laid-open (Unexamined) No. Sho 52-42434 (1977) discloses a method of forming a corrosion-resistant chemical conversion coating on an aluminum surface by dipping an aluminum surface in a treatment solution comprising an alkaline earth metal salt, an alkali metal sulfate and a carbonate or a bicarbonate. Nevertheless, the surface having the chemical conversion coating does not exhibit a sufficient corrosion resistance in a corrosive environment, e.g., that which causes an adhesion of an aqueous solution containing chloride ions, such as seawater to the surface.